Control units in motor vehicles may be used, for example, to activate ignition end stages external to the control unit. To this end, the control units may be controlled by a microprocessor. To ensure faultless operation, it may be required to implement a watchdog function, i.e., to read out and analyze status reports or diagnostic information from the control unit and to initiate appropriate measures, if required.
A device for monitoring a motor vehicle testing system is referred to in German Published Patent Application No. 40 32 926. This device is understood to include a testing device and a portable diagnostic unit, which may be interconnected via an interface. Moreover, a monitoring device may be provided, which may be connected to the testing device via the interface instead of the diagnostic device.
The device may be a simple device for monitoring a motor vehicle system. The user may obtain information concerning whether a fault is present in the diagnostic device or within the testing device.
A device for monitoring the function of an electrical switch configured as an end stage, its connected consumer, its activation, and the associated connecting lines is described in European Published Patent No. 0 477 309.
The device is understood to have at least one fault detection logic connected parallel to the end stage. A reference potential may be applied to the connecting point between the switch and the consumer. In addition, the potentials of the input and output terminals of the end stage as well as the reference potential may be applied to the fault detection logic. Based on the applied potentials, the fault detection logic may differentiate between faults such as short-circuit to positive terminal, load shedding, and short-circuit to ground. Moreover, a supplementary circuit may be provided for the storage of the fault status and for a control unit to input a fault log.
The device described may reliably differentiate between possible fault cases such as short-circuit to ground, short-circuit to positive terminal and load shedding. Proper function of the consumer and its activation may also be recognized.
In the event of a short-circuit or load shedding of the electronic units or ICs (primarily end stages) contained in control units, the diagnostic information may be read out via a serial interface.
The diagnostic interface (DI) has a data input, a data output, an input for the clock signal (CLK), and an input for synchronization (SYNC). The communication between the microcontroller and the electronic unit via this interface may require the setting and erasing or reading out from ports.
The SPI interface (serial peripheral interface) may allow communication, for example, between a microprocessor and an electronic unit such as an IC.
The communication may begin with the microprocessor setting a synchronization input of the electronic unit using a slave select (SS). The synchronization input “low” may be set to start the communication.
The clock signal (CLK) used to synchronize the data transmission may then be applied. The data input of the electric unit may be identified as MOSI (master out slave in) and the data output as MISO (master in slave out).
In contrast to the diagnostic interface, the SPI interface may be supported by microcontrollers or microprocessors. Sending and receiving may be accomplished by writing into and reading from registers.
The operation of the diagnostic interface may result either in the programming of wait loops in order to observe the bit times or a function procedure call per bit in the case, for example, of operation in the 1 ms pattern. This may tie up a large amount of microprocessor resources, which should be avoided, if desired.
If, however, it is desired to utilize the advantages of SPI, then it may be required to redesign ICs in control units. For ICs for which there may be no reason for redesigning except for the interface, this may be expensive. The present invention proceeds from this point.